This invention provides means for the pilot of a piston engine airplane to take manual control of the throttle when an electrical failure causes the electronic fuel system to malfunction.
The fuel system of an airplane can be divided into two parts, namely, the aircraft portion and engine portion. The aircraft portion includes the fuel tanks, the fuel booster pumps, the fuel drains, the fuel lines, the gages, the vents and filler caps, and the flow selector valves. The engine portion of the fuel system includes all the fuel controlling units between the engine driven pump supplied from the fuel lines and the point where fuel-air charge is fed into the engine cylinders. This includes the fuel flow control units and the carburetor or other fuel metering device. This invention is part of the engine fuel system.
The various ways that the fuel-air charges are prepared and delivered to the cylinders of an aircraft type piston engine are explained in the text authored by R. D. Bent and J. L. McKinley, titled Aircraft Powerplants, Fourth Edition, published 1978 by the Gregg Division of McGraw-Hill Book Co. This text covers basic fuel systems and both float-type and pressure injection carburetors. Fuel-injection systems are also discussed.
As explained on page 72 of the above referenced text . . . carburetors used on aircraft engines are comparatively complicated because they play an extremely important part in engine performance, mechanical life, and the general efficiency of the airplane. This is caused by the widely diverse conditions under which airplane engines are operated. The carburetor must deliver an accurately metered fuel-air mixture for engine loads and speeds between wide limits and provide for automatic or manual mixture correction under changing conditions of temperature and altitude. (The carburetor)...is subjected to continuous vibration that tends to upset the calibration and adjustment.
Most carburetors have a throttle valve incorporated in the fuelair duct either upstream or downstream of the main fuel discharge nozzle. The throttle valve is usually an oval-shaped metal disk mounted on the throttle shaft in such a manner that it can completely close the throttle bore. In the closed position, the plane of the disk makes an angle of about 70 degrees with the axis of the throttle bore. The edges of the throttle disk are shaped to fit closely against the sides of the fuel-air passage. The amount of air flowing through the venturi tube is reduced when the valve is turned toward its closed position. This reduces the suction in the venturi tube, so that less fuel is delivered to the engine. When the throttle valve is opened, the flow of the fuel-air mixture to the engine is increased. Opening or closing the throttle valve thus regulates the power output of the engine.
The goal with all carburetors whether of the float types or the pressure injection types is to automatically and accurately meter the fuel at all engine speeds and loads regardless of changes in altitude, propeller pitch, or throttle position. Recent innovations have brought about the development of electronic fuel control systems to better accomplish the automatic fuel metering task. This is fine except when a catastrophic failure occurs in the electrical system of the aircraft. For such a failure, improbable as such an occurrence might be, means must be found to allow the airplane pilot to take manual control of the engine throttle when there is a malfunction in the electronic system. My invention does this.